1. Field of the Invention
Present invention relates to a method of producing a silicon single crystal thin film on a semiconductor single crystal substrate in vapor-phase growth.
2. Related Art
An apparatus shown in FIG. 2, for example, is generally used for performing a method of producing a silicon single crystal thin film (hereinafter simply referred to as a thin film) on a semiconductor single crystal substrate (hereinafter simply referred to as a substrate) in vapor-phase growth.
In the figure, a vapor-phase growth apparatus 10 has a transparent quartz glass vessel 16 with a gas supply port 14 and a gas exhaust port 15 both opening in the vessel 16. The substrate 11 is placed on a susceptor 12 inside the quartz glass vessel 16.
The substrate 11 rotates on a rotary shaft 13, while it is heated by radiation heating means 18 mounted above and below the quartz glass vessel 16. After the substrate 11 is heated up to a temperature, at which a thin film is grown on the substrate in a satisfactory manner, for example of 800.degree. C. to 1200.degree. C., a process gas 20 comprising a carrier gas and a reactant raw material gas is fed to a main surface of the substrate 11 and thereby the thin film is grown on the main surface of the substrate 11 by a chemical reaction of the process gas 20.
It has been known that fine peaks and valleys are sometimes presence to on a surface of a silicon single crystal thin film in vapor-phase growth of the thin film and that the peaks and valleys are more amplified in size as the thickness of the thin film increases. No clear cause for the phenomena of amplification, however, has been known. An estimation has been accepted that a surface of a thin film would be oxidized by water molecules and the oxidized surface would be then reduced by hydrogen gas to create fine pits on the surface of the thin film, in the presence of water inside the vapor-phase growth apparatus for producing the thin film. Because of the inevitable presence of water, investigation through experiments on any imaginable causes other than the presence of water has not been able to be performed. It has been also known from experiences that the surface condition of the thin film varies between very smooth and very poor even in an ambient of a constant water concentration. As described above, because of no clear knowledge about causes and a creation mechanism of the peaks and valleys, a smooth surface of a silicon single crystal thin film has not been produced in vapor-phase growth in a stable manner.
The inventor has made extensive research on a chemical reaction for growing a silicon single crystal thin film. The following are findings, insights from and knowledge related to the findings. Silicon chloride raw material mixed with hydrogen gas is very often used when silicon single crystal thin films are industrially produced.
When any one of silicon chlorides for industrial usage is used, usually silicon tetrachloride (SiCl.sub.4), trichlorosilane (SiHCl.sub.3) or dichlorosilane (SiH.sub.2 Cl.sub.2), hydrogen chloride is generated as a by-product. Hydrogen chloride has a corrosive character as is well known, and a surface of a thin film grown is subject to corrosion by the hydrogen chloride gas.
The inventor of the present invention has studied about a way to use silicon chloride raw materials, since the materials are safer in handling compared with silane (SiH.sub.4) in light of the safety in handling, it is more advantageous to use silicon chlorides as the raw material if the corrosive character of the materials can be suppressed sufficiently.
According to the law of mass action, which is one of the fundamental rules in chemistry, it should be effective to suppress the corrosive action of hydrogen gas by making decomposition products of silicon chloride raw material generated together with hydrogen chloride to absorb onto the surface of the thin film. Based on these insights and knowledge, the inventor has reached to an idea as set forth below.
When trichlorosilane as an example of silicon chloride is used in a growth reaction of a silicon single crystal thin film, SiCl and/or SiCl.sub.2 is generated and adsorbed on the surface of the thin film, while hydrogen chloride is liberated, wherein trichlorosilane (SiHCl.sub.3) is decomposed in the vicinity of the surface, as illustratively shown in FIG. 3.
It would be reasonably accepted that the corrosive reaction of hydrogen chloride with a thin film is suppressed if SiCl and/or SiCl.sub.2 is adsorbed on the surface of the thin film, since hydrogen chloride reacts with SiCl and SiCl.sub.2 so as to give a priority on a reverse reaction of decomposition. In order to make SiCl and/or SiCl.sub.2 adsorbed on the surface of the thin film sufficiently, a growth rate has to be large enough by supplying silicon chloride raw material abundantly.